1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a method for manufacturing a vertical CMOS image sensor.
2. Discussion of the Related Art
In general, an image sensor is a semiconductor device which converts an optical image into an electrical signal. Image sensors are largely classified as a charge coupled device (CCD) or a complementary metal oxide silicon (CMOS) image sensor.
The CCD has a complicated drive system, has considerable power consumption, and requires a multi-step photo process. Moreover, it is disadvantageous in that a process of manufacturing the CCD is complicated. In particular, in the CCD, it is difficult to integrate a control circuit, a signal processing circuit, an analog/digital (A/D) converter, etc. on a CCD chip. Hence, it is difficult to reduce a size of the CCD.
Recently, a CMOS image sensor has been given attention as a next-generation image sensor that can overcome the disadvantages of the CCD.
The CMOS image sensor manufactured by a general CMOS process has advantages of low power consumption, a simple manufacturing process, low cost, and high integration.
The above-mentioned conventional CMOS image sensor is formed to have a stack structure including photodiodes and transistors. First, after a silicon epitaxial layer is formed, RGB color photodiodes are formed. Then, transistors are formed. Then, metal lines and via holes are formed. Then, after an upper metal layer is etched, a passivation oxide film and a passivation nitride film are formed by sequentially stacking the films. After the stack structure is completed, annealing is performed at a temperature of, generally, 400° C.
The conventional CMOS image sensor still has a problem of dark leakage characteristics. That is, the dark signal levels of the CMOS image sensor are still larger than those of a CCD manufactured by an optimal manufacturing process.